Method of lubricating an aluminum workpiece

ABSTRACT

An improved highly simplified method of lubricating an aluminum workpiece for subsequent working wherein a coating of complex alkaline earth metal aluminates is first formed and then a suitable lubricant is applied to the coating.

United States Patent [191 Bushey et al.

[4 1 Jul 22, 1975 METHOD OF LUBRICATING AN ALUMINUM WORKPIECE [75] Inventors: Albert 11. Bushey Ewell E. McDole,

both of Danville, Calif.

[73] Assignee: Kaiser Aluminum & Chemical Corporation, Oakland, Calif.

[22] Filed: May 18, 1973 [21] Appl. No.: 361,763

[52] U.S. Cl l48/6.27; 117/134 [51] Int. Cl C231 7/06; C23f 17/00 [58] Field of Search 148/627; 204/38 A, 58;

[56] References Cited UNITED STATES PATENTS 1,751,213 3/1930 McCulloch 148/627 X Primary Examiner-Ralph S. Kendall Assistant Examiner lohn D. Smith Attorney, Agent, or Firm-Paul E. Calrow; Edward .1. Lynch [57] ABSTRACT An improved highly simplified method of lubricating an aluminum workpiece for subsequent working wherein a coating of complex alkaline earth metal alu minates is first formed and then a suitable lubricant is applied to the coating.

8 Claims, No Drawings METHOD OF LUBRICATING AN ALUMINUM WORKPIECE BACKGROUND OF THE INVENTION This invention generally relates to the cold forming of aluminum products and in particular relates to an improved method of applying lubricant to an aluminum workpiece to be forged.

In the cold forging of aluminum products, prior practices, usually involved formed a chemical conversion coating on the workpiece, applying a lubricant to the conversion coating and then forging the workpiece into the desired shape usually by press forging, impact forging and the like. The conversion coating acts as a carrier for the forging lubricant and in many commercial systems, the lubricant actually reacts with the conversion coating. The prior art methods of forming the conversion coating required numerous steps which were difficult to control from the standpoint of quality and because of the difficulties in quality control, the process was not too reliable. A typical prior art sequence of steps for forming a conversion coating and applying a lubricant would be as follows:

1. Clean with a mild alkaline cleaner and rinse.

2. Etch in a caustic solution, then rinse.

3. Deoxidize and desmut in a 50% nitric acid solution, then rinse.

4. Clean in a mild alkaline cleaner, then rinse.

5. Treat with a suitable solution to form a conversion coating on the surface of the workpiece, then rinse.

6. Neutralize any residual acidity remaining after the last rinse.

7. Apply lubricant to the surface.

Most, if not all, of the above solutions must be frequently monitored for composition, temperature and the like to obtain reasonably reproducible results. Moreover, the spent solutions present an expensive and difficult disposal problem.

Against this background, the present invention was developed.

DESCRIPTION OF THE INVENTION The present invention provides an improved and a simplified method of lubricating an aluminum workpiece in preparation for subsequent cold working, such as drawing and forging operations. The invention comprises forming a lubricant carrying coating on the workpiece by treating the workpiece in an alkaline solution of alkaline earth metal compounds and then covering or impregnating the coating on the workpiece with a suitable lubricant. The coating which forms in this process is a complex alkaline earth metal aluminate coating which is characterized by a petalled surface under microscopic examination. A suitable method of forming this coating is described and claimed in U.S. Pat. No. 3,726,721 to Wittrock et al., and this patent is hereby incorporated herein in its entirety. The process is relatively easy to control and spent solutions pose no substantial disposal problems. The coating of the present invention when treated with a suitable lubricant provides for adequate lubrication during the entire cold forming operation even with a substantial amount of cold work.

As described in Wittrock et al., the alkaline earth metal aluminate coatings are generally prepared by treating an aluminum surface with an alkaline solution of alkaline earth metal salts. Initially, as evidenced by the evolution of hydrogen, the surface of the aluminum workpiece is etched, but this reaction quickly subsides and the complex aluminate coating begins to form. Process treatment times can range anywhere from about 10 seconds up to about 60 minutes, usually about 2-15 minutes, but the reaction is essentially complete after about 15 minutes. Extended treatment times, such as up to 4 hours, do not have any significant detrimental effects on the coating. Maximum coating thickness is about 0. 15 mil. The process is relatively simple to operate, control of the bath composition is minimal and spent solutions can be readily discarded with little or no treatment.

The treating solution is an alkaline solution of soluble alkaline earth metal compounds selected from the group consisting of soluble calcium, magnesium, barium and strontium compounds. Suitable compounds include the chlorides, nitrates, acetates and hydroxides. The concentration of the alkaline earth metal compound should be greater than 0.1 M, preferably greater than 0.2 M., and the hydroxide ion concentration should not be less than 0.005 M. An excessive amount of alkaline earth metal salt does not detrimentally affect the process. Preferably, the alkalinity of the solution is generated from sodium hydroxide, potassium hydroxide or lithium hydroxide, although under certain conditions, the alkalinity can be generated from the alkaline earth metal compound itself, such as with strontium hydroxide. The process is easily controlled by maintaining the alkaline earth metal concentration and the hydroxyl ion concentration at the point wherein the alkaline earth hydroxide begins to precipitate, although the process does not operate at levels considerably below the saturation point for the alkaline earth metal hydroxide. The pH generally must exceed 8.5, preferably greater than 9. Generally, the temperature of the bath should be maintained from about F., preferably from about F., to the boiling point of the solution (about 210F.). As described by Wittrock et al. in U.S. Pat. No. 3,726,721, the preferred treating bath is a boiling aqueous solution of an alkali metal hydroxide, such as sodium hydroxide, and a soluble calcium salt, such as calcium chloride, at concentrations at the point of calcium hydroxide saturation. The bath materials are cheap, readily available chemicals.

Other alkaline solutions of alkaline earth metal salts, such as described by McCullough in U.S. Pat No. 1,751,213, can be employed in the present invention, but as mentioned by Wittrock et al., these solutions do not work well (if at all) on a large scale where there is a high ratio of workpiece surface to volume of the bath apparently because of transient depletion of reacting component adjacent the workpiece surface resulting in a powdery coating which has little or no adhesion to the aluminum surface. To this extent, these powdery nonadherent coatings formed are not beneficial as a lubricant carrier, and are more or less equivalent to the powdery lime coatings used in the prior art practice many years ago in which the lime was applied as a lime slurry. (See U.S. Pat No. 1,963,298.)

Because the surface of the aluminum workpiece is initially etched with the treatment of the present invention, the numerous cleaning steps characteristic of the prior art coating methods are unnecessary, although in some cases, it may be desirable to degrease the aluminum surface with an inhibited alkaline cleaner or the like prior to treatment.

The tenacious coating formed in the present invention has been identified by x-ray Spectroscopy as an array of compositions ranging from the simple alkaline earth metal aluminates to complex aluminate double salts. The following compounds have been identified in coatings formed in a calcium chloride-sodium hydroxide bath: 3CaO.Al O .6H O; 3CaO.Al O .CaCO .l 1- H O; 3CaO.Al O .CaCl l 2H O; 3CaO.Al O CaCl .l3H O. Although the waters of hydration for the complex double salts are described above as l 1, l2 and 13, respectively, the amount of water of hydration can vary from 8 to 15. The carbonate double salt is formed due to the adsorption into the solution of carbon dioxide from the atmosphere.

The process in accordance with the present invention is most conveniently carried out by submerging the aluminum surface to be treated into the above-described bath until the desired thickness of coating is obtained. The coating can also be formed by spraying the alkaline solution onto the aluminum workpiece. However, in this instance, the concentration of the components and the temperature of the components should be toward the high side of the range. To minimize depletion of the active ingredients in the bath by carbonate formation, it is preferred to spray the solution with an airless-type jet.

After formation of the coating in the alkaline solution, the workpiece is rinsed, preferably dried, then treated with suitable lubricants which include metal soaps, such as zinc, lead, tin and magnesium soaps, and other metal-working lubricants. It is also found advantageous to employ a soap, such as potassium or sodium tallow soap, which form an alkaline earth metal soap in situ. Most commercially available lubricants can be employed, such as the various Bonderlubes manufactured by the Parker Division of Hooker Chemical Corporation. The lubricants can be applied in any conventional fashion. It may be applied as is, as an aqueous solution, an aqueous emulsion or dispersion or the like.

The thus-treated aluminum workpiece is then cold formed in the usual methods, such as by cold forging or drawing. The adherent coating of the present invention provides adequate lubrication even in extreme cases of metal deformation during cold forming. After deformation, the coating can easily be removed by treating in an acid solution, such as 50% nitric acid solution.

The following examples are provided as a further illustration of the present invention and no limitations are implied therefrom.

A treating solution was prepared containing about 25 gm/liter of CaCl about 1 gm/liter of NaOH and the balance essentially water and heated to boiling. Samples of 3004 (O temper) aluminum alloy were treated in the bath for 2, l and 50 minutes to form a complex calcium aluminate coating thereon, and then each sample was coated with a lubricant. The lubricants used were Bonderlube 233, an epoxidized soybean oil, a mixture of oleic acid 1 part) and polybutene (9 parts). Disks 2% inches in diameter were blanked from the samples and then drawn into cups with a 33 mm diameter punch on a Ductomatic Tester. All samples indicated excellent lubrication.

A second treating solution was prepared as above and employed in coating aluminum forging workpieces. Treatment times in the boiling solution averaged about 10 minutes. The coated products were rinsed, dried and the coating impregnated with Bonderlube 233 which had been heated to about 155F. for application. The aluminum products were cold forged into a variety of shapes with all indications that thelubrication was excellent.

It is obvious that various modifications and improvements can be made to the present invention without departing from the spirit of the invention, as well as the scope of the appended claims.

What is claimed is:

1. A method of applying a lubricant to an aluminum workpiece prior to the cold working thereof consisting essentially of:

a. forming a tenacious coating of complex alkaline earth metal aluminates on the surface of the aluminum workpiece by treating said workpiece in an alkaline solution at a temperature of at least F containing at least 0.1 gram/mol per liter of a soluble alkaline earth metal compound selected from the group consisting of calcium, barium, strontium and magnesium compounds; and

b. applying a metal working lubricant onto said formed coating.

2. The method of claim 1 wherein said solution contains at least 0.005 gram mol per liter of an alkali metal hydroxide selected from the group consisting of potassium hydroxide, sodium hydroxide and lithium hydroxide.

3. The method of claim 2 wherein said alkaline earth metal compound is a calcium salt selected from the group consisting of calcium chloride, calcium nitrate, and calcium acetate.

4. The method of claim 1 wherein said lubricant includes an alkali metal soap which reacts with the complex alkaline earth metal aluminate coating on the surface of said workpiece and forms an alkaline earth metal soap therewith.

5. The method of claim 1 wherein said workpiece is treated in the alkaline solution for a period of greater than 1 minute.

6. The method of claim 3 wherein said alkaline solution is at a temperature from about 100F. to the boiling point of the solution.

7. A method of applying a lubricant to an aluminum workpiece prior to the cold working thereof consisting essentially of:

a. degreasing the surface of the aluminum workpiece;

b. forming a tenacious coating of complex alkaline earth metal aluminates on the surface of the aluminum workpiece by treating said workpiece in an alkaline solution at a temperature of at least 100F containing at least 0.1 gram/mol per liter of a soluble alkaline earth metal compound selected from the group consisting of calcium, barium, strontium and magnesium compounds; and

c. applying a metal working lubricant onto said formed coating.

8. A method of applying a lubricant to an aluminum workpiece prior to the cold working thereof consisting essentially of:

a. forming a tenacious coating of complex alkaline earth metal aluminates on the surface of the aluminum workpiece by treating said workpiece in an alkaline solution at a temperature of at least l0OF containing at least 0.1 gram/mol per liter of a soluble alkaline earth metal compound selected from the group consisting of calcium, barium, strontium and magnesium compounds;

b. rinsing the formed coating; and

c. applying a metal working lubricant onto said formed coating. 

1. A METHOD OF APPLYING A LUBRICANT TO AN ALUMINUM WORKPIECE PRIOR TO THE COLD WORKING THEREOF CONSISTING ESSENTIALLY OF: A. FORMING A TENACIOUS COATING OF COMPLEX ALKALINE EARTH METAL ALUMINATES ON THE SURFACE OF THE ALUNINUM WORKPIECE BY TREATING SAID WORKPIECE IN AN ALKALINE SOLUTION AT A TEMPERATURE OF AT LEAST 100*F CONTAINING AT LEAST 0.1 GRAM-MOL PER LITER OF A SOLUBLE ALKALINE EARTH METAL COMPOUND SELECTED FROM THE GROUP CONSISTING OF CALCIUM, BARIUM, STRONTIUM AND MAGNESIUM COMPOUNDS, AND B. APPLYING A METAL WORKING LUBRICANT ONTO SAID FORMED COATING.
 2. The method of claim 1 wherein said solution contains at least 0.005 gram mol per liter of an alkali metal hydroxide selected from the group consisting of potassium hydroxide, sodium hydroxide and lithium hydroxide.
 3. The method of claim 2 wherein said alkaline earth metal compound is a calcium salt selected from the group consisting of calcium chloride, calcium nitrate, and calcium acetate.
 4. The method of claim 1 wherein said lubricant includes an alkali metal soap which reacts with the complex alkaline earth metal aluminate coating on the surface of said workpiece and forms an alkaline earth metal soap therewith.
 5. The method of claim 1 wherein said workpiece is treated in the alkaline solution for a period of greater than 1 minute.
 6. The method of claim 3 wherein said alkaline solution is at a temperature from about 100*F. to the boiling point of the solution.
 7. A method of applying a lubricant to an aluminum workpiece prior to the cold working thereof consisting essentially of: a. degreasing the surface of the aluminum workpiece; b. forming a tenacious coating of complex alkaline earth metal aluminates on the surface of the aluminum workpiece by treating said workpiece in an alkaline solution at a temperature of at least 100*F containing at least 0.1 gram/mol per liter of a soluble alkaline earth metal compound selected from the group consisting of calcium, barium, strontium and magnesium compounds; and c. applying a metal working lubricant onto said formed coating.
 8. A method of applying a lubricant to an aluminum workpiece prior to the cold working thereof consisting essentially of: a. forming a tenacious coating of complex alkaline earth metal aluminates on the surface of the aluminum workpiece by treating said workpiece in an alkaline solution at a temperature of at least 100*F containing at least 0.1 gram/mol per liter of a soluble alkaline earth metal compound selected from the group consisting of calcium, barium, strontium and magnesium compounds; b. rinsing the formed coating; and c. applying a metal working lubricant onto said formed coating. 